The present invention relates to an image forming apparatus arranged to bring a charger, such as a charging roller, into contact with a photosensitive member to charge the photosensitive member and form an electrostatic latent image on the charged photosensitive member so as to form an image. More particularly, the present invention relates to an image forming apparatus incorporating a cleaner for cleaning a charger and arranged to remove foreign matter, such as toner, allowed to adhere to the charger.
An image forming apparatus, such as an electrostatic copying machine and a printer, incorporates a charging unit for charging a photosensitive member. Hitherto, corona charge has widely been adopted to the charging unit. The corona charge, however, suffers from a problem of a defect of a formed image because ozone or nitrogen oxide is formed which adheres to the surface of the photosensitive member or the like.
Therefore, a charger apparatus adapted to a contact charging method has been disclosed in, for example, Japanese Patent Publication No. 63-49668A. The foregoing method is arranged to bring a charger to which voltage is applied and which is constituted by, for example, urethane rubber into contact with the photosensitive member so as to charge the photosensitive member. The foregoing contact charging method is able to overcome the problem experienced with the foregoing corona charge.
The contact charging method is arranged such that the charger is in contact with the photosensitive member. Therefore, the contact charging method encounters adhesion of foreign matter to the surface of the charger, the foreign matter being, for example, toner on the photosensitive member, undesirably allowed to pass through the cleaning unit or toner separated from the developing unit. Therefore, defective charge of the photosensitive member occurs, causing the quality of the formed image to deteriorate.
Therefore, pieces of image forming apparatus of a type incorporating a cleaner for removing foreign matter, such as toner, allowed to adhere to the surface of the charger have been suggested. When the cleaner of the image forming apparatus is always in contact with the charger, the surface of the charger sustains damage. In the foregoing case, defective charging occurs. Therefore, the cleaner is disposed such that contact and separation with respect to the charger are permitted. The cleaner is brought into contact with the charger only when the charger is cleaned. When the charger is not cleaned, the cleaner is separated from the charger. Usually, the charger is periodically cleaned when a printing operation is not performed. For example, in Japanese Patent Publication No. 7-128954A, the charger is cleaned whenever a predetermined number of image forming operations has been performed. In Japanese Patent Publication No. 7-128956A, the charger is cleaned at intervals of predetermined time.
A variety of pieces of image forming apparatus have been suggested in, for example, Japanese Patent No. 2853208. The foregoing image forming apparatus has a structure that the photosensitive member, the development unit and the cleaning unit are accommodated in a single process cartridge. The process cartridge is detachably mounted on a predetermined position in the body of the image forming apparatus. When the photosensitive member or the like deteriorates, the process cartridge is changed.
The related image forming apparatus incorporating the member for cleaning the charger and arranged to use a detachable process cartridge has a structure that the cleaner is provided for the body of the image forming apparatus without exception.
When the cleaner is provided for the body of the image forming apparatus, (1) since the cleaner is provided for the purpose of removing foreign matter, such as toner, allowed to adhere to the charger, cleaning conditions including the contact load at which the cleaner is brought into contact with the charger and the position of contact must be optimized. Since the cleaner is provided for the body of the image forming apparatus, optimization of the cleaning conditions cannot easily be performed because cleaning conditions are undesirably varied. As a result, the life of the charger is shortened undesirably. When the contact load is too large, the surface of the charger sustains damage. When the contact load is too small, the performance for removing foreign matter, such as toner, deteriorates.
(2) Since the cleaning unit must be changed individually from change of the process cartridge, a user must bear a heavy load, such as labor for changing the cleaning unit.
Besides, when foreign matter, such as toner, adheres to the charger, the foregoing deterioration in the image does not occur. That is, the density of the output image is sometimes changed. In the foregoing case, the charger is not cleaned with the cleaner. That is, the density of the image is adjusted to correct the change in the density of the image. The correction is realized by patch control (charging bias or a development bias is adjusted in the foregoing case).
The patch control is, as disclosed in, for example, Japanese Patent Publication No. 7-111591B, performed to correct change in the density of an image in a case where the density of the image is changed according to change in the use environment and length of the operation time.
When change in the density of an image occurring when foreign matter, such as toner, adheres to the charger is corrected by the foregoing patch control, an operation for cleaning the charger which is performed after the patch control has been performed sometimes results in change in the density of the image in spite of completion of the adjustment of the density of the image by performing the patch control.
Besides, a cleaning unit incorporating a mechanism for permitting contact/separation of the cleaner and arranged to clean the charger has a structure that toner removed from the charger by the cleaner is accumulated in a nip portion in which the charger and the cleaner are in contact with each other when the cleaner is separated from the charger. A portion of toner is moved to the photosensitive member. Therefore, when the operation of the photosensitive member is interrupted at arbitrary timing, removed toner is sometimes left on the photosensitive member. When the image forming apparatus has started a printing operation in the foregoing state, movement of toner removed and left on the photosensitive member to the transferring position undesirably causes toner to be transferred. Thus, there arises a problem in that an image defect occurs.
Therefore, when the cleaner periodically cleans the charger, occurrence of an image defect caused from transference of toner removed and left on the photosensitive member must be prevented.
In general, an electrophotographic method is arranged to bring a rubber blade into contact with a photosensitive member under a predetermined pressure so as to remove residual toner on the photosensitive member after an image has been transferred therefrom. Abrasion between the photosensitive member and the rubber blade causes the leading end of the blade to repeat small mechanical vibration during the operation. In cases where the vibrations are amplified, a defect state of cleaning occurs momentarily. Thus, residual toner is sometimes leaked downstream of the blade. Thus, toner adheres to the charging roller, causing contamination to occur.
Hitherto, the contamination of the charging roller has been prevented by the following suggested methods.
(1) a method with which a cleaner is pressed against the charging roller to mechanically remove contamination (for example, Japanese Patent Publication No. 6-342237A); and a method with which a cleaner is vibrated in the axial direction of a charging roller to improve cleaning efficiency (for example, Japanese Patent Publication No. 7-110618A);
(2) a method with which toner allowed to adhere to the charging roller is uniformed to prevent occurrence of line-shape contamination which causes a problem image (for example, Japanese Patent Publication No. 7-168422A).
Since the charging roller is constituted by resin, rubber or the like, the foregoing method (1) with which contamination is mechanically removed requires a structure that a pad, rubber, sponge or the like is employed as the cleaner to remove contamination. Therefore, it is very difficult to remove toner allowed to adhere the surface of the charging roller. Although toner can be removed when the cleaner is strongly pressed against the charging roller, the surface of the roller easily sustains damage. When the cleaner is pressed with a low pressure to prevent damage of the surface of the roller, toner is undesirably left in the form of lines on the surface of the charging roller. Therefore, the contact pressure between the cleaner and the charging roller cannot easily be adjusted.
The foregoing method (2) with which adhesive toner is uniformed is a method of removing toner. As the apparatus is used, contamination is gradually accumulated. Thus, the charging roller is covered with toner. Therefore, a radical countermeasure against contamination cannot be realized.
In view of the foregoing, the first object of the present invention is to provide an image forming apparatus capable of reliably and easily optimizing cleaning conditions and reducing the load which must be borne by a user when the changing operation or the like is performed.
The second object of the present invention is to provide an image forming apparatus capable of preventing exertion of an influence of the operation of the cleaner in a case where the patch control is performed.
The third object of the present invention is to provide an image forming apparatus arranged to prevent transference of toner in a case where toner removed by a cleaner is left on the photosensitive member so as to prevent an image defect caused from removed toner.
The fourth object of the present invention is to prevent contamination of the charger so as to form an image having high quality.
In order to achieve the above objects, according to the present invention, there is provided an image forming apparatus comprising:
a photosensitive member on which an electrostatic latent image is to be formed;
a rotative charger brought into contact with the photosensitive member to charge the same;
a cleaner brought into contact with the charger to clean the same;
a cleaner driver for bringing the cleaner into contact with the charger and for separating therefrom; and
a single cartridge detachably provided in the image forming apparatus for accommodating the photosensitive member, the charger, the cleaner and the cleaner driver.
Since the photosensitive member, the charger, the cleaner and the cleaner driver are accommodated in a single process cartridge, the position accuracy between the charger and the cleaner can considerably be stabilized. Hence it follows that the cleaner can reliably and substantially uniformly be brought into contact with the charger. It leads to a fact that the cleaning conditions under which the cleaner cleans the charger can furthermore reliably and easily be optimized.
Since the cleaner driver and the cleaner are accommodated in the same process cartridge, any mechanical connection between the cleaner driver and the cleaner is not required when the cleaner is accommodated in the process cartridge as compared with a structure that the cleaner driver is provided in the body of the image forming apparatus. Therefore, only electrical connection with the power source in the body of the image forming apparatus is required. Hence it follows that the cleaning conditions can be made to be stable and facilitated in spite of the operation of the cleaner which is brought into contact with the charger and separated from the same. As a result, foreign matter, such as toner, allowed to adhere to the surface of the charger can furthermore reliably be removed. Since only the electrical connection is required, the structure between the cleaner driver and the cleaner can be simplified. It leads to a fact that the cost can be reduced.
Since the foreign matter on the surface of the charger can furthermore reliably be removed, the life of the process cartridge accommodating the cleaner and the cleaner driver can be elongated.
Since the cleaner, the cleaner driver, the photosensitive member and the charger are accommodated in a single process cartridge, the accommodated units can substantially and easily be replaced. Thus, a user""s load can be reduced.
Preferably, the cleaner driver brings the cleaner into contact with the charger to execute the cleaning operation at least immediately before a patch control for adjusting the density of image to be formed is performed.
Accordingly, foreign matter, such as toner, has been removed from the surface of the charger when the patch control is performed. In the foregoing case, the density of the image is adjusted by the patch control. Then the charger is not cleaned. Hence it follows that stable and satisfactory image quality can be maintained until a cleaning operation which is performed immediately before the next patch control.
Preferably, the photosensitive member is provided as a photosensitive drum. The photosensitive drum is rotated after the cleaner which has terminated the cleaning operation has been separated from the charger, and continues rotating until a portion of the photosensitive member, which corresponds to the portion from which the cleaner has separated, passes a position where a developed image thereon is to be transferred onto an image transfer member.
In this case, even if some of toner removed by the cleaner has been moved to the surface of the photosensitive member, toner present on the photosensitive member can reliably pass through the image transfer position. Therefore, when the image forming apparatus performs an image forming operation after the cleaner has completed the operation for cleaning the charger, the toner is not transferred. Thus, occurrence of an image defect can be prevented.
Alternatively, the photosensitive drum is rotated at least one time alter the cleaner, which has terminated the cleaning operation, has been separated from the charger.
In this case, even if some of toner removed by the cleaner has been moved to the surface of the photosensitive member, toner present on the photosensitive member can reliably be removed by the cleaning unit. Thus, when the image forming apparatus performs an image forming operation after the cleaner has completed the operation for cleaning the charger, transference of the toner can be prevented. As a result, occurrence of an image defect can reliably be prevented.
Preferably, the cleaner is brought into contact with the charger with a contact pressure which is enough to float residual toner adhered onto the charger, and not enough to allow the floated toner to pass through to a downstream portion of the cleaner.
Preferably, wettability of the charger with respect to toner used for developing the latent image is lower than that of the photosensitive member.
In this case, the toner allowed to adhere to the charger is floated to reduce the intermolecular force of the toner with respect to the charger to allow passing of the toner to the downstream position. Because the wettability of the photosensitive member with respect to the toner is made to be larger than that of the charger with respect to the toner, the toner which is allowed to move to the downstream position of the charger is moved to the photosensitive member. Therefore, contamination of the charger can effectively be removed.
Preferably, the wettability of the charger is larger than that of the cleaner.
In this case, adhesion of the toner to the cleaner does not easily occur. Thus, passing of the toner from the cleaner can efficiently be performed. As a result, contamination of the charger can effectively be reduced.
Preferably, the cleaner is provided as a brush member having a predetermined contact width in the rotational direction of the charger.
In this case, since the cleaner can uniformly be brought into contact with the charger without any gap, toner having reduced intermolecular force can frequently be produced. Since scraped toner can be accumulated in the fibers of the brush member, contamination of the peripheral portion can be reduced. Moreover, the accumulated toner is not permanently trapped in the fibers. That is, the toner can be discharged to the downstream position.
Preferably, the contact pressure of the cleaner is within a range from 0.1 g/cm to 30 g/cm.
Preferably, the cleaner has conductivity.
In this case, an abnormal discharge phenomenon caused from accumulation of electric charge can be prevented. Thus, contamination of the peripheral portion with toner caused from the abnormal discharge can be prevented.
Preferably, hardness of the surface of the charger is represented as 2H or higher of the pencil hardness.
In this case, frequency of piercing of the fluidizer can be reduced. Therefore, contamination of the charger can be prevented. As a result, the cleaning efficiency can be improved.
Preferably, the cleaner is separable from the charger.
In this case, since the cleaner is not always in contact with the charger, damage of the charger is not sustained by the cleaner. Therefore, fatigue of the cleaner can be prevented.
Preferably, a potential of the charger is made floatable when the cleaner is brought into contact with the charger.
In this case, electrostatic adhesivity of toner to the charger and that to the photosensitive member can be made to be the same. Therefore, toner can efficiently be moved to the photosensitive member.
Preferably, the cleaner is moved in an axial direction of the charger while the charger is rotated.
In this case, even toner allowed to adhere to the charger with large intermolecular force can be floated because the intermolecular force can be reduced more effectively.
Preferably, the cleaner is provided as a brush member leading ends of which are engaged with the charger. The distance for which the cleaner is moved is longer than the engagement depth of the cleaner.
In this case, the leading ends of the brush member can be moved and slid with respect to the charger. The large intermolecular force with which the toner is allowed to adhere can be reduced.
Preferably, the distance for which the cleaner is moved is longer than a contact width between the charger and the photosensitive member.
In this case, uniformity of charging caused by the charger can be improved.